The present invention generally relates to an apparatus and method to dice integrated circuits by high-pressure fluid jet, and more specifically to an apparatus and method to dice integrated circuits such as planar light-wave circuits from a wafer by an abrasive water jet.
Planar light-wave circuits are increasingly used in many optical and electro-optical systems (e.g., computer systems, programmable electronic systems, telecommunication switching systems, control systems, and so forth). A planar light-wave circuit (PLC) can be fabricated on a wafer by processes nearly identical to the processes used to fabricate electronic integrated circuits on a semiconductor wafer. In some cases PLCs may be fabricated on rectangular pieces of a wafer like electronic integrated circuit chips, but in many cases PLCs are preferably fabricated on irregularly shaped pieces of a wafer in order to increases the PLC yield from each wafer.
FIG. 1A illustrates part of a wafer containing an array of identical, irregularly shaped PLCs 102, 104, 106, 108, 110, 112, and 114. Each PLC contains a non-rectangular structure that does not completely fit in a rectangular sample cut from the wafer by cuts 116 and 118 (shown as dotted lines). FIG. 1B shows how conventional rectangular die cutting will result in the cutting and loss of several PLCs, where only PLC 110 is intact and PLCs 106, 108, 112, and 114 have been damaged. The PLC wafer yield and resulting fabrication cost for contains a non-rectangular structure that does not completely fit in a rectangular sample cut from the wafer by cuts 116 and 118 (shown as dotted lines). FIG. 1B shows how conventional rectangular die cutting will result in the cutting and loss of several PLCs, where only PLC 110 is intact and PLCs 106, 108, 112, and 114 have been damaged. The PLC wafer yield and resulting fabrication cost for each PLC would be greatly improved by a dicing apparatus and method for cutting a wafer into separate non-rectangular dice. FIG. IC illustrates one PLC 102, which has been precisely cut from the wafer.
However, the cutting of wafers into such irregular shapes is extremely difficult with conventional wafer dicing methods and apparatus (i.e., a rotating abrasive blade saw). Conventional wafer dicing methods and apparatus are particularly inadequate for cutting a die with non-rectangular edges. Laser cutting can be used to cut irregularly shaped dice from a wafer, but laser cutting has several disadvantages. These disadvantages include very high equipment and operational costs, and poor edge quality resulting from thermal stresses and differential absorption of laser energy by various structures and layers on the wafer. The poor edge quality of the laser die cutting can create fractures in a die that ultimately propagate towards the center of the die, and thereby create operational and reliability problems.
There is an unmet need in the art to use a low cost apparatus and method to cut irregularly shaped dice from a wafer in order to increase the yield of dice from each wafer and reduce the unit cost of fabricating the dice.
There is also an unmet need in the art to have an apparatus and method to cut a die with high quality edges that do not propagate fractures into the operational areas of the die.
The invention provides a low cost apparatus and method to cut irregularly shaped dice from a wafer in order to increase the yield of dice from each wafer and reduce the unit cost of fabricating the dice
The invention also provides an apparatus and method to cut a die with high quality edges that do not propagate fractures into the operational areas of the die.
A first aspect of the invention is directed to a method to cut irregularly shaped dice from a wafer. The method includes placing the wafer on a fixture; aligning the wafer in the fixture to expose the dice to a fluid jet cutting nozzle; expelling the abrasive in combination with the fluid from the fluid jet cutting nozzle at a velocity sufficient to cut through the wafer, while the fluid jet cutting nozzle moves in relation to the wafer in the fixture; and removing the dice from the fixture after the dice have been cut from the wafer.
A second aspect of the invention is directed to an apparatus to provide a wafer die cutting system to cut a wafer. The apparatus includes a fixture to align and hold the wafer; a cutting nozzle to expel a fluid and an abrasive towards the wafer at a velocity sufficient to cut through the wafer; a fluid source to supply the fluid to the cutting nozzle; an abrasive source to supply the abrasive to the cutting nozzle; and a mechanism to move the cutting nozzle relative to the wafer.
These and other advantages of the invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
FIG. 1A illustrates part of wafer containing an array of identical, irregularly shaped planar light-wave circuits (PLCs).
FIG. 1B shows how conventional rectangular die cutting will result in the cutting and loss of several PLCS, where only one PLC is intact and four other PLCs have been damaged.
FIG. 1C illustrates one PLC, which has been precisely cut from the wafer.
FIG. 2 illustrates one embodiment of the invention using a segmented wafer.
FIG. 3 illustrates one embodiment of the invention for a fixture.
FIG. 4 illustrates another embodiment of the invention, which uses a fluid jet cutting system having a visual alignment system.
FIG. 5 illustrates one embodiment of a wafer with alignment marks for visual alignment by means of one or more cameras.
FIG. 6 illustrates one embodiment of a cutting head assembly.
FIG. 7 shows a flow chart to align and cut a wafer on a fluid jet cutting system in accordance with one embodiment of the invention.
FIG. 8 shows a flow chart to cut dice from a wafer in accordance with another embodiment of the invention.